It is well known that conventional manufacturing processes conduct the reaction of reactants and the separation of products in reactors and distillation columns separately. Such processes have the following disadvantages: too many operational steps, large investment for the fabrication of equipment, the reaction heat cannot be used and an additional cooling system is needed to take away the reaction heat so as to maintain the reaction temperature constant. When these processes are used for reversible reactions, due to the limited conversion of the equilibrium reaction, such processes need to repeat the reaction-distillation procedure for two or more times to obtain the desired conversion of the reactants.
A catalytic distillation process has been developed to simplify the process mentioned above and to utilize the reaction heat during the reaction-distillation procedure. The reaction of the reactants and the distillation of products are carried out in the same catalytic distillation column, the products being distilled out as soon as they are formed. As a result, the reaction tend equilibrium can be broken which makes the reaction toward completion and increase the conversion of the reactants. In addition, the reaction heat can be absorbed by the evaporation of the reactants. Therefore, not only can the reaction temperature can be maintained constant, but also the energy consumption of the process can be greatly reduced.
A typical catalytic distillation column contains three sections: a rectifying section at the upper part, a catalytic reaction section at the middle part and a stripping section at the lower part of the column. In said column, it is obvious that the stream of liquid phase and the stream of vapor phase flow countercurrently through said catalytic reaction section and undergo reaction and distillation in said section. However, when the particle size of the catalyst is too small, the flow resistance of the catalyst beds will be too great and makes the liquid and vapor streams difficult to pass through the reaction section countercurrently, which causes the reaction-distillation process very difficult to continue.
Several methods for packing catalyst have been developed to solve the above problems. U.S. Pat. No. 3,434,534 teaches to put catalyst into liquid downcomers of distillation trays as additional reactors. According to this process, the amounts of catalyst loaded in said downcomers are limited. U.S. Pat. No. 4,471,154 proposes to use catalyst capsules, in which catalyst is enclosed in a fabric cloth or a cloth of intercrossed stainless wires permeable to liquid but impermeable to catalyst particles having a shape of rectangular or other form, and distribute these capsules on the distillation trays in the distillation column. The reactants diffuse into the capsules and react on the catalyst surface inside the capsules as it flows across the distillation trays. This method also limits the amount of catalyst and does not promote the reaction of the reactants due to the diffusion resistance of the capsules to the reactants and the products. Similarly, U.S. Pat. No. 4,215,011 discloses a method of using catalyst capsules, in which catalyst is in a number of fabric cloth bags, the bags being packed in the catalytic reaction zone with channels between these capsules so that the liquid and vapor can countercurrently flow through said catalytic reaction zone. U.S. Pat. No. 4,847,430 proposes to use a reaction-distillation zone containing at least two superposed and noncontiguous fixed beds of catalyst, wherein passageways are provided for a vapor phase and at least one distillation tray and at least two liquid redistribution trays are between the fixed beds. Reactant in the liquid phase react under the action of catalyst as they flow through catalyst beds downwardly and undertake the heat and mass transfer on the distillation trays. The disadvantages of the method are the complexity of the structure of the column, the limited amount of the catalyst loaded due to the occupation of space by the distribution and distillation trays between said beds, and the lower reaction efficiency due to the reduction of the concentration of reactants and contact time of the reaction materials with the catalyst by mixing the charge of reactants with the liquid materials coming from the rectifying section. U.S. Pat. No. 3,579,309 discloses a "Column for carrying out organic chemical reactions in contact with fine particulate catalyst". According to this patent, a plurality of catalyst receiving reactors are arranged outside the two sides of the column respectively. In nature, it is a column that a plurality of non-contiguous reactors are disposed outside said column and between a plurality of pairs of distillation trays. U.S. Pat. No. 4,089,752 discloses a "Distillation column reactor and process", said column reactor comprising a distillation column containing standard trays with downcomers, a liquid reservoir, whereby liquid from said downcomers enters said reservoir thereby providing increased residence time in said column. It is used for a homogeneous phase reaction. U.S. Pat. No. 4,624,748 discloses "Catalyst system for use in a distillation column reactor", said column including an annularly-defined space within the reactor comprised of vapor-permeable material with packed catalyst and alternately positioned vapor barrier means. In such a system, the flow resistance between upwardly flowing vapor phase and downwardly flowing liquid phase is quite significant; and since the inner and outer wall forming the annularly-defined catalyst bed are perforated plates, and both the vapor and liquid phase can pass through the perforated plates, or liquid may be taken out by vapor phase, which make operation and entire system unworkable.